Pervious concrete, also referred to as porous concrete, permeable concrete, no-fines concrete, gap-graded concrete, or enhanced-porosity concrete, is a composite material comprising coarse aggregate, Portland cement, and water. The coarse aggregate is bonded together at its points of contact by a layer of paste formed by the cement and water, forming a connected network of open pores or voids that lets fluids drain through the cured material. Pervious concrete mixes typically include the same materials as are used in ordinary concrete mixes, but in different proportions. In pervious concrete, water and cementitious material are combined such that a thick paste coats the aggregate particles. Fine aggregates is reduced or eliminated, and a narrowly sized coarse aggregate is used. The reduced cementitious paste content and absence of fine aggregates prevent close packing between the coated coarse aggregate particles, and a hardened structure containing open and connected voids is obtained.
Pervious concrete allows rainwater to percolate through a formation into the ground below. By capturing rainwater and allowing it to seep into the ground, pervious concrete helps to reduce stormwater runoff contamination in downstream waterways and to recharge groundwater supplies. Sensitivity to the adverse effects of stormwater contamination has greatly expanded the use of pervious concrete. EPA regulations under the federal Clean Water Act, as well as regional, state, and local standards, increasingly incorporate the use of pervious concrete as a best management practice to reduce stormwater runoff and improve water quality. Thus demand for pervious concrete continues to grow as a material of choice for parking lots, driveways, pedestrian paths, walkways, sidewalks, plazas, borders, pavement, retaining walls, and other structures that accumulate and discharge stormwater into the environment.
The mix characteristics of pervious concrete require careful placement and curing to maximize strength and durability of a pervious formation. The reduced cementitious content of pervious mixes produces concrete having relatively lower strength than non-pervious formations, but requiring more curing time to develop sufficient strength to withstand loading. At the same time, the thin coating of paste on the aggregate, the open structure, and the rough surface of pervious concrete increase evaporation of the water in the paste needed for the bonding reactions of the cement. To cure correctly, pervious concrete are moistened and covered typically for at least seven days. For pavement applications that will see traffic in service, it is generally recommended that the pavements not be opened to construction or public traffic for seven days, and continuous curing is recommended until the pavement is opened, disrupting work schedules, delaying project completion, and increasing costs. See, e.g., ACI 522.1-08, Specification for Pervious Concrete Pavement, published by the American Concrete Institute. A need remains for a pervious concrete mix that can cure to load-bearing strength more quickly and be opened to traffic sooner than current mixes allow.